This invention relates to an improved process for producing high purity 1-hydroxyethyl-2-undecyl-2-imidazoline, which is an intermediate in the manufacture of surfactants.
In the prior art, it was well known that 1-hydroxyethyl-2-undecyl-2-imidazoline could be prepared by the reaction of lauric acid and aminoethylethanolamine. For example, in U.S. Pat. No. 2,528,378 (the '378 patent) equimolar amounts of lauric acid and aminoethylethanolamine (AEEA) were reacted in the liquid phase and the water of reaction was distilled off to drive the reaction to completion.
That process, however, was not satisfactory because unwanted diamides were formed which precipitated and grained out from solutions at room temperature. This made the final products manufactured from the imidazoline unacceptable for use in commercial products, such as, cosmetics.
In order to overcome this problem, it was proposed in U.S. Pat. No. 3,408,361 (the '361 patent) that the reaction be performed using a large excess of the diamine with the addition, during the process, of additional amounts of the diamine well below the surface of the reaction mass. In the '361 patent, this addition was considered mandatory because in the process described, the diamine was lost overhead along with the water of reaction. The amount of amine added each period was "at least equal to the amount . . . which [would] be distilled out before the next addition [was] made" (column 5, lines 40 to 44). This procedure, while reducing the diamide formation, proved cumbersome and unnecessarily complicated the process for forming the desired product.
In order to overcome the foregoing drawbacks, applicants have discovered that 1-hydroxyethyl-2-undecyl-2-imidazoline may be prepared by a straightforward process giving products of high purity. This is accomplished by initially charging the fatty acid to the reaction zone along with a molar excess of the diamine. By using a first distillation zone having vapor-liquid contact area, the water may be removed overhead without the loss from the system of more than trace amounts of the diamine. Subsequently, when the reaction is substantially complete, the vapor from the reaction zone is fed to a second distillation zone whereby at least some, and usually most, of the remaining unreacted AEEA may be removed. This second zone is substantially devoid of any vapor-liquid contact area. The product remaining in the reaction zone after the excess diamine is removed is of high purity.